Update VM Initializer for Netbox 2.7

The vm database model has changed in Netbox 2.7.
Therefore the initializer code, that was used before, broke.
As a user, you will need to update your virtual_machines.yml
file as follows:

- Make sure the status is spelled lowercase.

See the diff of this commit for further information how this is meant.

initializers/prefixes.yml

@@ -1,13 +1,22 @@
+## Possible Choices:
+##   status:
+##   - container
+##   - active
+##   - reserved
+##   - deprecated
+##
+## Examples:
+
 # - description: prefix1
 #   prefix: 10.1.1.0/24
 #   site: AMS 1
-#   status: Active
+#   status: active
 #   tenant: tenant1
 #   vlan: vlan1
 # - description: prefix2
 #   prefix: 10.1.2.0/24
 #   site: AMS 2
-#   status: Active
+#   status: active
 #   tenant: tenant2
 #   vlan: vlan2
 #   is_pool: true
@@ -15,6 +24,6 @@
 # - description: ipv6 prefix1
 #   prefix: 2001:db8:a000:1::/64
 #   site: AMS 2
-#   status: Active
+#   status: active
 #   tenant: tenant2
 #   vlan: vlan2